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BX Trianguli AB: A binary star with the shortest orbital period among main-sequence stars.

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BX Trianguli is a binary system made up of two red dwarfs, in the constellation Triangulum. Both stars eclipse each other and have an orbital period of four hours and 40 minutes. They are located at around 170 light-years from Earth based upon parallax measurements.

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This system is composed of two red dwarfs, which have an ultra-short period of just 4.6 hours and a separation of 1.33 solar radii, or two and a half times the distance to the Moon. This orbit is one of the shortest known among main sequence stars. The primary star, named BX Trianguli A, has a mass equivalent to 58% the solar mass and a radius equivalent to 60% of the solar radius, while the secondary BX Trianguli B is smaller, at 28% and 27% of the solar mass and radius respectively. BX Trianguli has a semi-detached configuration, with the "A" component being distorted due to gravitational interactions with its partner.

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A circumbinary planet was discovered after analysis of eclipse timing variations by a high school student and his teacher. After ruling out alternative expanations for the eclipse timing variations, the two discoverers found that they are caused by a seven-Jupiter-mass planet at a separation of 4.5 astronomical units (670,000,000 km), with an orbital eccentricity of 0.4. The findings were published in 2024 at the American Association of Variable Star Observers's 113th Annual Meeting.